Path: utzoo!attcan!uunet!husc6!wuarchive!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request
From: bill@vrdxhq.verdix.com (William Spencer)
Newsgroups: rec.audio.high-end
Subject: Re: Quad ESL63 and Subwoofer
Message-ID: <5503@uwm.edu>
Date: 2 Aug 90 12:50:16 GMT
Sender: news@uwm.edu
Lines: 38
Approved: tjk@csd4.csd.uwm.edu


in article <5447@uwm.edu>, FCFIFRAGA%CIUC2.UC.RCCN.PT@CUNYVM.CUNY.EDU (FRANCISCO AMARAL F FRAGA) says:

> I have heard several experiments of ELS63
> with subwoofers and I was not fully pleased. [...]
> If some one has experience or information of home building subwoofers
> and matching active crossovers for Quad ELS63 I would be quite
> pleased to hear about.

Check out _Speaker Builder_ #6/89. The system described has two 
very interesting features:

* Dipole type subwoofer. This helps solve the integration problems of
  matching dipole main speakers. Interesting, since dipoles are not known
  for bass. However there are advantages: the driver operates at free air 
  resonance and the polar response is different. The author of the article
  used a single Hartley 24" driver. I could see using multiple low cost
  15" woofers instead to get the required "cubic inches" of air movement.
  The cabinet (open back) was only a bit larger than the driver
  and rolls off at 6 dB
  per octave below 100 Hz due to baffle cancellation. The author claims
  the efficiency is high.

* Use of combined electronic and acoustic rolloffs for the crossover.
  This could be useful in any subwoofer system. The Quads roll off at
  12 dB per octave below 80 Hz. The elecronic crossover adds 6 dB/octave
  to provide a combined 18 dB/octave slope at 80 Hz. The subwoofer side uses 
  an 18 dB/octave filter using Old Colony filter boards plus the 
  6 dB/octave boost below 100 Hz to compensate for the baffle cancellation
  noted above. The 6 dB filter for the mains only provides a small reduction
  in the Quad's workload but it still helps. More signifigant, the filter
  is passively implemented so none of your main tone need pass through 
  excess circuitry.

The above info should help with one of the most common questions on the 
net. I'm planning on some dipole experiments myself soon (not for Quads :-).

bill S.